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Archive for May, 2016

Forester: TPMS FTW, Sorta-Kinda

According to the Forester’s manual, the Tire Pressure Monitoring System kicks in after the car reaches 25 mph. It evidently takes a while to figure things out after that, because the TPMS light blinked on a mile from home on the way to Mary’s Vassar Farms garden. I pulled into the next parking lot, measured 20 psi in the left rear tire, then found this staring me in the eye:

Forester - left rear tire with screw

Forester – left rear tire with screw

Well, that certainly simplified the diagnosis!

I unloaded two bags of shredded leaves and a pile of hoses, swapped in the (limited use, donut-style) spare tire, and continued the mission.

The TPMS light wasn’t on when I drove to Squidwrench the previous evening. Judging from the wear, that screw appeared during the various errands following our 800 mile road trip, which is good news of a sort, and depressurized the tire over the course of a day or two.

The receipt from the fix-it folks cautions that a plug is a temporary fix, because “the injury has compromised the integrity of the tire”. On the other paw, the Forester manual tells me “All four tires must be the same in terms of manufacturer, brand (tread pattern), construction, and size. You are advised to replace the tires with new ones that are identical to those fitted as standard equipment” and then provides a checklist:

When you replacing or installing tire(s), all four tires must be the same for following items.
(a) Size
(b) Circumference
(c) Speed symbol
(d) Load index
(e) Construction
(f) Manufacturer
(g) Brand (tread pattern)
(h) Degrees of wear

There’s absolutely no way to get an identical replacement tire, let alone one with the same tread wear, but I am so unready to replace all four tires after 12 k miles / 2 years.

We shall see how this works out…

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Groundhog on High Alert

Looks like I’m getting the stinkeye:

Groundhog being suspicious

Groundhog being suspicious

The extensive garden armor remains effective, although we know groundhogs can run straight up a chain-link fence when given sufficient motivation. They generally give up after encountering the galvanized chickenwire around the buried concrete blocks; the garden is just to the left of the picture.

The front-yard groundhog suffered a fatal automobile accident shortly after it finished excavating its burrow against the front foundation. This critter may have moved into the abandoned summer home near the garage at the back of the house.

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Blender Bearing Repair: Round Three

After half a dozen years, the bearings in the blender impeller felt pretty bad:

Defunct blender bearings

Defunct blender bearings

I wiped everything clean, found the box containing the box containing the tube of bearings, packed the base with more silicone grease, reassembled everything in reverse order, and it’s all good again.

The first repair lasted for a year and the second for six, so I think overpacking the base with grease helped a lot. Maybe I’m getting better at ignoring horrible grinding sounds.

I can do this twice more, although the Jesus clip holding the shaft into the bearing stack definitely needs replacing.

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Monthly Image: Transit of Mercury

The 2016 Transit of Mercury, as seen from Red Oaks Mill:

Mercury transit - 2016-05-09

Mercury transit – 2016-05-09

Hint: Mercury is (almost certainly) the tiny speck below and left of the crosshair.

The larger speck is (almost certainly) Sunspot 12529, one of the few in this part of a historically weak Solar Cycle. Its shape would be obvious though a real telescope.

If you know what you’re doing, you can measure the size of the sun and scale the entire solar system from observations like that. Takes more science than I’ll ever accomplish, that’s for sure!

I realized the show was on just before Greatest Transit (roughly what you see above), so I duct-taped a 1 inch spotter / finder scope to a camera tripod, taped a sun shield on the scope, bent some card stock for a screen, then assembled everything on the patio:

Mercury transit - 2016-05-09 - spotting scope setup

Mercury transit – 2016-05-09 – spotting scope setup

Astronomy mostly happens at night; this was an unexpected delight!

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Hard Drive Platter Mood Light: Failed LED Debugging Assistance

Another of the knockoff Neopixels in the Hard Drive Platter Mood Light failed, even limited to PWM 63 to reduce the temperature. This time, however, I had some help finding the failed blue LED:

Hard Drive Mood Light - failed LED with spider - green

Hard Drive Mood Light – failed LED with spider – green

Spiders seem no less bizarre in white light:

Hard Drive Mood Light - failed LED with spider - white

Hard Drive Mood Light – failed LED with spider – white

A day later, she’d built a small web, presumably to improve the odds of catching something yummy. Who am I to disagree?

I should set up a test fixture for all the knockoff Neopixels and run some numbers. They’re definitely a disappointment, even to a bottom feeder such as I …

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Hiatus

After devoting the last few months to setting up the Makerspace Starter Kit and extracting / organizing / stashing the stuff I wanted to keep:

New parts cabinets

New parts cabinets

I now have some difficulty accomplishing what needs to be done:

Basement Shop - right

Basement Shop – right

During the rest of May I must write a pair of columns, unpack / arrange / reinstall my remaining tools / parts / toys, endure a road trip to our Larval Engineer’s graduation (*), enjoy bicycling with my Lady, and surely repair a few odds-n-ends along the way.

I’ll generate occasional posts through June, after which things should be returning to what passes for normal around here…

(*) For reasons not relevant here, our Larval Engineer’s schedule includes a final co-op and wind-up semester after “graduation”. Perhaps she’s entering the Chrysalis phase of her development?

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Audio Direction Finding

Given a point source of audio (or RF, for that matter) that’s far enough away to produce more-or-less plane wavefronts, the range difference between two microphones (or ears) is:

ΔR = (mic separation) x sin Θ

The angle lies between the perpendicular to the line from the midpoint between the mics counterclockwise to the source source: + for sounds to your left, – for sounds to your right. That’s the trig convention for angular measurement with 0° directly ahead, not the compass convention, but you can argue for either sign if you keep track of what’s going on.

The time delay between the mics, given c = speed of sound:

ΔT = ΔR / c

For microphones 300 mm apart and c = 344 m/s:

ΔT = 872 µs = 0.3 m / 344 m/s

If you delay the sound from the mic closest to the source by that amount, then add the mic signals, you get a monaural result that emphasizes, at least a little bit, sounds from that source in relation to all other sounds.

In principle, you could find the angle by listening for the loudest sound, but that’s a fool’s game.

There’s an obvious symmetry for a source on the same side, at the same angle, toward the rear.

A GNU Radio data flow diagram that lets you set the angle and listen to / watch the results:

Audio Direction Finding.grc

Audio Direction Finding.grc

The original doodles show it takes me a while to work around to the answer:

Audio direction finding doodles

Audio direction finding doodles

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